Research On Underground Power Loss Line Fault Detection Method Based On Additional Power Electronic Power Supply

China adopts the power supply system with ungrounded underground neutral point,which is difficult to achieve the selective leakage protection.However,once the non-selective leakage protection has a leakage fault,it will cause the main feeder switch to trip.The fault detection of the power-loss lines often uses a more time-consuming opening-line method,which will cause the consequences of too long blackout time in the mine.If the fault detection and line selection of the multi-branch system with power failure can be performed quickly,the outage time will be greatly shortened.In addition,if the loss of power line with unknown fault is directly put into the system for use without fault detection,it will lead to many adverse consequences,such as circuit breaker tripping,or even safety accidents.Therefore,it is of great significance to study the fault detection of underground power loss line.This paper aims to propose a fault diagnosis scheme based on power electronic disturbance technology which can accurately and quickly implement the fault diagnosis of the underground power loss line.First of all,the common faults of the underground line can be divided into asymmetric faults and symmetric faults.The corresponding fault detection principle and fault criterion for various types of faults are proposed separately.The additional AC power supply forms different detection circuits by injecting detection signals into the line and controlling the thyristor conduction to detect different faults.Single-branch and multi-branch impedance models are established,which form different loops for the detection signals.The equivalent circuit diagram is used to study the principle of fault detection.For asymmetric faults,a fault detection method based on detecting the current signal waveform is proposed.By analyzing the amplitude and direction of the signal waveform,the leakage faults and interphase faults can be detected.Using the area method based on the signal waveform,the fault criterion is established.For symmetrical faults,a detection method based on system harmonic reactance is proposed,which can detect the harmonic reactance obtained by Fourier transform of transient voltage and current signals.By analyzing the variation trend of harmonic reactance under different harmonics,the symmetrical faults in the line can be detected.According to the comparative analysis of the slope of the line fitted based on the variation trend,the symmetric fault criterion is established.Second,the injection method,frequency and amplitude of the detection signal,the thyristor conduction scheme,and the fault detection process are all designed and selected according to the actual operating environment.The safety of the fault detection scheme during operation also needs to be fully considered to ensure that the detection scheme will not cause personal electric shock during operation.Considering the harsh operating environment,the detection scheme should include the explosion-proof design,including the installation of explosion-proof enclosure.Through the non-explosive evaluation method,the detection circuit is proved to be intrinsically safe.Considering that the leakage blocking device is put into operation simultaneously after the underground feeder trips,this paper also studies its impact on the fault detection scheme.In the end,Matlab software is used to build underground lines for the simulation analysis of the principles of fault detection schemes.The analysis results show that the detection principle proposed in this paper can accurately detect all kinds of underground faults,and can realize fault line selection under multiple branches.